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P0721: Output speed sensor: range/performance

The gearbox output speed does not match wheel or engine speed; usually a dirty sensor, a poor contact or electrical interference.

Code P0721 at a glance
CodeP0721
SystemEngine and transmission
GroupP07xx, Transmission
TypeGeneric: it means the same on every make
Can you keep driving?With care

What P0721 means

The output speed sensor measures how fast the shaft leaving the gearbox towards the wheels is turning. The control unit uses it to decide when to shift and, on many cars, it also feeds the speedometer or other systems. This code means the signal arrives but is not consistent: it jumps, drops out at times or does not fit the speed measured by other sensors, such as the ABS ones.

Most common causes

  • Sensor covered in metal particles or not fitted securely
  • Loose or corroded connector
  • Damaged or poorly shielded wire picking up interference
  • Tyres of a different size from the original
  • Faulty sensor
  • Transmission control unit fault (uncommon)

Symptoms

  • Speedometer failing, flickering or dropping to zero
  • Harsh or oddly timed shifts
  • Gearbox stuck in one gear (limp mode)
  • Engine or gearbox warning light on

Can you drive with P0721?

With care You can drive with care, but the gearbox usually locks into one gear and acceleration suffers. Get it to a garage soon and avoid long trips like this.

How to check it

Check whether the speedometer works properly: if it fails at the same time as the code appears, it points to the output sensor or its wiring. On the scanner you can compare the vehicle speed reading with a GPS.

How to read and clear P0721 with Final OBD

Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0721 with this same explanation and whether it’s confirmed, pending or permanent.

This code is usually stored by the gearbox control unit. With Free you read it for nothing with its short description, because Free reads every control unit; with Pro you also get the full explanation, how the car was running when it was logged and clearing.

Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.

Similar codes

P0721 is a generic code, so it means the same on any make, for example on Abarth, Cupra, Hyundai, Jeep, Mini, Seat. See what Final OBD does on your car in makes and models.

What does code P0721 mean?

The output speed sensor measures how fast the shaft leaving the gearbox towards the wheels is turning. The control unit uses it to decide when to shift and, on many cars, it also feeds the speedometer or other systems. This code means the signal arrives but is not consistent: it jumps, drops out at times or does not fit the speed measured by other sensors, such as the ABS ones.

Can you drive with P0721?

You can drive with care, but the gearbox usually locks into one gear and acceleration suffers. Get it to a garage soon and avoid long trips like this.

How do you clear P0721?

With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0721 comes back.